many plants of serissa should be SerissE!

No, I'm sorry, but Serissa is not an Italian word. It is the Latin name of a
plant. If you want to use colloquial English, you could say Serissas, but it is
more correct to say one Serissa or several Serissa, but nothing else.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)